1. Field of the Invention
The present invention relates generally to a feedthrough for an optical fiber, and, more particularly, to such a feedthrough providing an hermetic seal about the optical fiber and a wall member through which it passes.
2. Description of Related Art
There are many situations in which it is desirable to pass an optical fiber cable through a wall member and secure the fiber to the wall member in such a manner that a hermetic seal is provided against the passage of fluids (e.g., air). This task is made especially difficult because of the importance in dealing with an optical fiber not to stress it or to produce micro-bending which can result in severe damage to the fiber or substantially reduce the quality of an optical signal being transmitted.
U.S. Pat. No. 4,119,363, PACKAGE FOR OPTICAL DEVICES INCLUDING OPTICAL FIBER-TO-METAL HERMETIC SEAL, by I. Camlibel, discloses an hermetic sealing technique for an optical fiber in which the fiber is located within an oversized tube 28 and secured therein by a quantity of metal solder. On cooling, the initially molten solder solidifies and squeezes against the fiber to form the desired hermetic seal.
A further hermetic sealing technique for use with a fiber optic is that disclosed in U.S. Pat. No. 4,214,809, FIBER OPTIC PENETRATOR, by Oswald R. Reh, in which a clearance passage, substantially larger than the fiber optic, is provided through a bulkhead separating two different pressure regions. A guide sleeve 19 is received within the bulkhead clearance passage which has an axial bore slightly larger than the diameter of the fiber optic received therein. Pressure plugs are provided at opposite ends of the guide sleeve which include sapphire orifice members with very small clearance for an inserted fiber optic, which clearances are sealed by using a resilient bonding agent.
Illustrative of yet another optical fiber feedthrough, U.S. Pat. No. 4,296,996 discloses inserting an optical fiber having a metal film coated thereon with an oxide outer surface through an oversized opening in an end face plate bore and filling the space between the inner wall of the hole with a thermoplastic material 3 such as polyethylene. A metal fitting 8 located on the high pressure side A will act to pressurize the thermoplastic material 3 to increase the seal between the material 3 and both the metal film 2 and the plate 4.